Skip Navigation


Author(s): Nancy Moreno, PhD, Barbara Tharp, MS, Deanne Erdmann, MS, Sonia Rahmati Clayton, PhD, and James Denk, MA.

Disease Information: Smallpox

Smallpox has been in the news quite a lot recently. Maybe you heard about it first after the terrorist attacks in 2001. Since then, there has been a lot of talk about the possible use of “biological weapons,” including smallpox, to infect and even kill a large number of people. 

An Ancient Nemesis 
Smallpox is a very contagious disease caused by the Variola (smallpox) virus. Scientists believe it originated in humans in India or Egypt more than 3,000 years ago. Since then, smallpox has been one of our deadliest diseases. Smallpox epidemics once spread throughout entire continents. (An epidemic is a widespread outbreak of a disease.) Many of those who got smallpox died, and some those who survived were blinded and physically marked by the disease with scars.

The name, “smallpox,” refers to the bumps that infected people get on their faces and bodies, and in their throats, mouths and noses. There are two common forms of smallpox: Variola major and Variola minor. (The word, “variola,” comes from the Latin word for “spotted.”) Both forms lead to sores on the skin, fever, headache and other flu-like symptoms. However, Variola major is a far more deadly disease. It is estimated that 30% of the people who have caught this illness have died.

Smallpox affects only humans. It does not make animals sick, and it is not transmitted by insects. There is no cure for smallpox, but there now is a vaccine that can prevent infection, even up to four days after a person has been exposed to the Variola virus. However, some people should not get the vaccine, including pregnant women and people with skin problems, a weakened immune system or some other medical problems. 

Chicken pox is not a mild form of smallpox. Although it causes similar (but less disfiguring) sores, it is caused by a different virus.

It’s in the Air
Most often, smallpox is transmitted when a person infected with the disease sneezes or coughs near someone else. If the infected person has a fever and rash, he or she is able to spread smallpox to others until the very last blister heals. The disease is easiest to spread during the 7–10 days after the rash first appears. Although smallpox is deadly, it takes direct and fairly prolonged face-to-face contact to spread smallpox to another person.

It also is possible to catch smallpox from contaminated objects, such as blankets or clothing. In very rare cases, smallpox has been spread through the ventilation systems of buildings, trains and other closed places. 

Usually, it takes 12–14 days for a person who has been exposed to smallpox to be able to spread the disease. During this time, the virus is multiplying inside the person and usually causes no symptoms. 

Some Risk Remains
Following a worldwide vaccination program, smallpox was eliminated globally by 1980. The last U.S. case was in 1949. But smallpox still exists in laboratories, so it is possible that another outbreak could occur. Since the disease has been eradicated (eliminated) for more than 25 years, almost no one has been vaccinated against it recently. Therefore, very few people have immunity. If there is an outbreak, it might not be possible to vaccinate every person exposed to smallpox in time to prevent them from being infected. This combination of factors makes any future smallpox epidemic extremely dangerous. The most recent cholera pandemic (worldwide outbreak) began in Asia in 1961. It spread to Europe and Africa and, by 1991, to Latin America, where there had been no cholera for more than 100 years. This outbreak has killed thousands of people and continues to spread. Cholera can be a risk for anyone traveling to places where outbreaks are occurring. 

Funded by the following grant(s)

Science Education Partnership Award, NIH

Grant Number: 5R25RR018605